The present invention relates to a support for supporting a substrate during processing in a plasma.
An ionized gas or plasma is used in many types of manufacturing processes, including for example, semiconductor fabrication processes. For example, plasmas are used in chemical vapor deposition, etching, and ion implantation processes. Referring to FIG. 1, a typical conventional plasma process chamber 20 comprises a gas distributor 30 for distributing process gas in the chamber for forming a plasma. The process gas plasma is energized by applying a RF voltage to a cathode 40a supporting a substrate 50 and by electrically grounding an anode 40b to form a capacitive RF field in the chamber. However, conventional plasma chambers often do not provide a spatially uniform plasma sheath across the surface of the substrate 50. By spatially uniform it is meant a plasma sheath having a uniform density and/or energy distribution of plasma ions across the space occupied by the plasma sheath. A non-uniform distribution of plasma ions often occurs due to variations in the RF or DC fields or currents (as represented by the arrows 80a, 80b) across from the center 60 to the peripheral edge 70 of the substrate 50.
For example, in certain chambers, the cathode 40a comprises a periphery that extends circumferentially around the substrate 50 and is electrically isolated from the plasma by a relatively thick insulator shield 90, as shown in FIG. 1. However, the insulator shield 90 isolating the periphery of the cathode 40a can significantly influence the RF currents between the cathode 40a and the plasma sheath near the peripheral edge 70 of the substrate 50. In other process chambers, the cathode 40a stops short of, and does not extend all the way to the peripheral edge 70 of the substrate (not shown). As a result the plasma sheath forms anomalies or discontinuities near the peripheral edge 70 of the substrate.
The non-uniform plasma ion distribution obtained across the surface of the substrate 50 in such conventional chambers can cause the peripheral edge 70 of the substrate (typically extending inwardly by a distance of 15 to 20 mm from the substrate edge) to be processed at different rates or with different properties relative to the central portion 60 of the substrate 50. For example, in etching processes, plasma anomalies can result in etched features having non-uniform sidewall profiles at the edge 70 of the substrate 50. This significantly reduces the yield of integrated circuit chips obtained from the peripheral edge 70 of the substrate 50. The lower plasma ion densities that can occur at the peripheral edge 70 of the substrate 50 also result in slower and less efficient processing of the peripheral edge 70 of the substrate.
Another disadvantage of conventional plasma process chambers arises from the substrate holding system 100 that is used to hold the substrate in the process chamber 20. Conventional holding systems 100 include mechanical clamps that hold the periphery of the substrate, vacuum systems, or electrostatic chucking systems. Mechanical clamps (not shown) cover the edge of the substrate and reduce substrate yields. Vacuum chucks (also not shown) can cause contamination of the substrate 50 from the flow of process gas and suspended particles toward the vacuum port behind the substrate. Electrostatic chucking systems, as shown in FIG. 1, typically comprise an electrically insulated electrode 110 that is positioned below the substrate 50 to electrostatically attract the substrate 50 using electrostatic charge. While electrostatic chucks solve certain problems of mechanical and vacuum chucks, they are often easily eroded in the chamber because the insulator covering the surface of the chuck is made of a polymeric material that is easily eroded in the plasma process gas. Also, electrostatic chucks require separate power supplies 120 and the electrode 110 of the chuck has to be entirely electrically insulated from the cathode 40a which lies below the chuck. Furthermore, the insulator material that surrounds the electrode 110 of the chuck, can reduce electrical coupling from the cathode 40a to the plasma sheath and/or the transfer of heat from the substrate 50 to the cathode 40a.
Thus, there is a need for an apparatus that provides a more spatially uniform plasma sheath across the surface of a substrate. There is also a need for the apparatus that extends the RF and DC field components in the chamber beyond the peripheral edge of the substrate to form a plasma sheath that also extends beyond the peripheral edge of the substrate. There is a further need for an apparatus that can electrostatically hold the substrate on a support and couple RF power to a plasma above the substrate, without requiring multiple overlying structures, such as the electrostatic chuck and cathode structures.